/*
  Twofish Cipher for KeePass Password Safe
  Copyright (C) 2009-2010 SEG Tech <me@gogogadgetscott.info>

  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Security;
using System.Security.Cryptography;
using System.Diagnostics;

using KeePassLib;
using KeePassLib.Cryptography.Cipher;

using TwofishCipher.Crypto;

namespace TwofishCipher
{
  public sealed class TwofishCipherEngine : ICipherEngine
  {
    private const CipherMode m_rCipherMode = CipherMode.CBC;
    private const PaddingMode m_rCipherPadding = PaddingMode.PKCS7;

    private PwUuid m_uuidCipher;

    public static readonly byte[] TwofishCipherUuidBytes = new byte[]{
            0xAD, 0x68, 0xF2, 0x9F, 0x57, 0x6F, 0x4B, 0xB9,
            0xA3, 0x6A, 0xD4, 0x7A, 0xF9, 0x65, 0x34, 0x6C
        };

    public TwofishCipherEngine()
    {
      m_uuidCipher = new PwUuid(TwofishCipherUuidBytes);
    }

    public PwUuid CipherUuid
    {
      get
      {
        Debug.Assert(m_uuidCipher != null);
        return m_uuidCipher;
      }
    }

    public string DisplayName
    {
      get { return "Twofish (256-Bit Key)"; }
    }

    private static void ValidateArguments(Stream stream, bool bEncrypt, byte[] pbKey, byte[] pbIV)
    {
      Debug.Assert(stream != null); if (stream == null) throw new ArgumentNullException("stream");

      Debug.Assert(pbKey != null); if (pbKey == null) throw new ArgumentNullException("pbKey");
      Debug.Assert(pbKey.Length == 32);
      if (pbKey.Length != 32) throw new ArgumentException("Key must be 256 bits wide!");

      Debug.Assert(pbIV != null); if (pbIV == null) throw new ArgumentNullException("pbIV");
      Debug.Assert(pbIV.Length == 16);
      if (pbIV.Length != 16) throw new ArgumentException("Initialization vector must be 128 bits wide!");

      if (bEncrypt)
      {
        Debug.Assert(stream.CanWrite);
        if (stream.CanWrite == false) throw new ArgumentException("Stream must be writable!");
      }
      else // Decrypt
      {
        Debug.Assert(stream.CanRead);
        if (stream.CanRead == false) throw new ArgumentException("Encrypted stream must be readable!");
      }
    }

    private static Stream CreateStream(Stream s, bool bEncrypt, byte[] pbKey, byte[] pbIV)
    {
      ValidateArguments(s, bEncrypt, pbKey, pbIV);

      Twofish f = new Twofish();

      byte[] pbLocalIV = new byte[16];
      Array.Copy(pbIV, pbLocalIV, 16);
      f.IV = pbLocalIV;

      byte[] pbLocalKey = new byte[32];
      Array.Copy(pbKey, pbLocalKey, 32);
      f.KeySize = 256;
      f.Key = pbLocalKey;

      f.Mode = m_rCipherMode;
      f.Padding = m_rCipherPadding;

      ICryptoTransform iTransform = (bEncrypt ? f.CreateEncryptor() : f.CreateDecryptor());
      Debug.Assert(iTransform != null);
      if (iTransform == null) throw new SecurityException("Unable to create Twofish transform!");

      return new CryptoStream(s, iTransform, bEncrypt ? CryptoStreamMode.Write :
          CryptoStreamMode.Read);
    }

    public Stream EncryptStream(Stream sPlainText, byte[] pbKey, byte[] pbIV)
    {
      return CreateStream(sPlainText, true, pbKey, pbIV);
    }

    public Stream DecryptStream(Stream sEncrypted, byte[] pbKey, byte[] pbIV)
    {
      return CreateStream(sEncrypted, false, pbKey, pbIV);
    }

  }
}
